1. Field of the Invention
This invention relates a method for producing ultra microparticles and ultra microparticles, and more particularly the same method and the same particles suitable for fundamental materials in a broad field of various catalysts such as photocatalyst and metallic catalyst, memory materials, luminescent materials, optoelectronics, etc.
2. Description of Related Art
Ultra microparticles having sizes of nm-scale (hereinafter, often abbreviated as xe2x80x9cnm-sizexe2x80x9d) made of semiconductor material or metallic material are regarded as important for fundamental materials in a broad field of various catalysts such as photocatalyst and metallic catalyst, memory materials, luminescent materials, optoelectronics, etc.
It is, however, very difficult for controlling particle size in nm-size and obtaining particles with small particle size-distribution. Thus, in the past, a method was employed that the growing of the particle size is inhibited by coexisting a surface-stabilizing agent such as a polymer, a surfactant, or a micelle with a dispersed quasi-stable semiconductor material or metallic material.
Besides, a method to control the particle size with matrix such as zeolite or clay mineral was employed. Moreover, a method to separate only desired microparticles with electrophoresis or size-excluding chromatograph after producing the ultra microparticles with a given particle size-distribution was employed.
However, the coexisting of a polymer, a surfactant or matrix such as zeolite results in condition-change of surfaces of the ultra microparticles or contamination of the ultra microparticles due to its additive. Consequently, the thus obtained ultra microparticles do not have desired characteristics when using them.
On the other hand, the method to separate with electrophoresis results in complicating an equipment for producing the ultra microparticles and their producing process, and rising up their producing cost.
Employing the above methods, microparticles with sub-nm size can be obtained, but the ultra microparticle with nm-size can not.
It is an object of the present invention to provide a producing method capable of obtaining the ultra microparticles with nm-size in ease and good reproducibility, and provide the ultra microparticles obtained via the producing method.
This invention relates to a method for producing ultra microparticles comprising steps:
dissolving or dispersing at least one of metallic salts into a solvent to form a solution, and
irradiating a microwave to the solution to produce the ultra microparticles made of a metal in the metallic salt.
These inventors have been intensely studied to obtain the nm-sized ultra microparticles. As a result, they found that by irradiating a microwave with a given intensity to a solution including a melted metallic salt, the nm-sized ultra microparticles can be produced in a short time. The present invention is realized on the above finding.
FIG. 1 is a graph showing a particle size-distribution of metallic Ni particles obtained from the producing method according to the present invention. As is apparent from FIG. 1, the particle size-distribution of metallic Ni particles shows a peak at a particle size of 7 nm and has an average particle size of 7 nm. Thus, according to the present invention, the ultra microparticles with nm-size can be easily produced.
The reason capable of easily producing the ultra microparticles with nm-size as above mentioned is not clear, but it is considered as follows:
When a microwave is irradiated to a dissolved or dispersed solution of a metallic salt, the metallic salt is excited absorbing the microwaves. As a result, the metallic salt may be reduced and resolved to produce colloids.
Herein, the above microwave in the present invention has a frequency of 2.45 GHz.